1. Field of the Invention
This invention is related to a method and device for making a metal bump with an increased height and in particular to one which can increase the connection reliability between the metal bump and the chip and enlarging the contact area between the metal bump and the metal or solder ball.
2. Description of the Prior Art
Various kinds of methods of making metal bumps on a chip have been developed for flip chip on board (FCOB) technology with a small number of input pins or a small number of Input/Output pins or for flip chip in package (FCIP) with a large number of Input/Output pins, such as evaporation plating, splash plating, electroplating, printing, spraying, and bonding. However, the capillary tube 2xe2x80x2 is still the most commonly used tool for making metal stud bumps by means of wire bonding (see FIG. 1A). As shown, the capillary tube 2xe2x80x2 has an inner diameter 21xe2x80x2 with an inner wall 22xe2x80x2 and has a larger diameter at the upper end than the lower end. A metal wire 3xe2x80x2 is inserted into the capillary tube 2xe2x80x2 and the lower end of the metal wire 3xe2x80x2 is melted to form a ball shaped member 31xe2x80x2 by electric spark. Then, ultrasonic vibration and pressure deformation processing are applied to the capillary tube 2xe2x80x2 to join the inter-metallic compounds between wire 3xe2x80x2 and the chip 1xe2x80x2 (see FIG. 1B). When the capillary tube 2xe2x80x2 is removed, a metal bump 32xe2x80x2 will be formed on the raised platform 11xe2x80x2 of the chip 1xe2x80x2 (see FIG. 1C). Thereafter; a metal or solder ball 4xe2x80x2 is soldered on the metal bump 32xe2x80x2.
However, due to the limitation of the design of the capillary tube 2xe2x80x2, the metal bump 32xe2x80x2 will have a spherical surface which is insufficient to provide a large contact area and a reliable structure for joining other component parts. Furthermore, the bottom of the metal bump 32xe2x80x2 will tend to go beyond the lower opening of the capillary tube 2xe2x80x2 under pressure thereby making it difficult to control. Moreover; as the metal bump 32xe2x80x2 has a spherical surface, there will not be sufficient area in contact with a metal or solder ball 4xe2x80x2 (see FIG. 1D). In addition, the metal bump 32xe2x80x2 is so short that the metal or solder ball 4xe2x80x2 must be soldered to the metal bump 32xe2x80x2 at a very low position thereby making it difficult to make the connection between the die and the fingers of a substrate (or lead frame, chips, metal bumps or the like) and therefore influencing the qualification rate of products.
Therefore, it is an object of the present invention to provide a method and device for making a metal bump with an increased height which can obviate and mitigate the above-mentioned drawbacks.
This invention is related to a method and device for making a metal bump with an increased height.
It is the primary object of the present invention to provide a method and device for making metal bumps with an increased height which can increase the joining strength with other metal bumps or pads of a die.
It is another object of the present invention to provide a method and device for making metal bumps with an increased height which can enlarge the contact area with the metal or solder ball.
It is still another object of the present invention to provide a method and device for making metal bumps with an increased height which can increase its reliability in joining with other component parts.
It is a further object of the present invention to provide a method and device for making metal bumps which have an increased height but are small in diameter.
The foregoing object and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts.
Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example.